Humidity control apparatus having an energy limiting power source



March 30, 1965 AMDUR 3,175,400

J. HUMIDITY-CONTROL APPARATUS HAVING AN ENERGY LIMITING POWER SOURCE Filed Sept. 12, 1961 7 f n 10 ug! 45' a @511, 52 so @V/IIIIA I V 51 41 "I In 4342 2 3 4 5 6 CURRENT INVENTOR. ELIAS J AMpzne JTTOENEV United States Patent 3,175,480 HUMIDETY CGNTROL APPARATUS HAVENG AN LiMiTlNG POWER SQURCE Elias J. Amdur, St. Louis Park, Minn assignor to Honeyweli inc, a corporation of Delaware Filed Sept. 12, 1961, Ser. No. 137,592 2 Claims. (Cl. 73336.5)

The present invention is concerned with an improved moisture responsive device; in particular, the moisture responsive device has a heated electrical circuit connected to a source of power so that an equilibrium temperature is maintained depending upon the moisture level of the surrounding air. The source of power has the characteristics to limit the heating efiect of the electrical circuit.

Moisture responsive devices comprising an electrical circuit connected to a source of power which contain a heating element in the electrical circuit changing in electrical resistance depending upon the moisture level of the surrounding air have been used for some time. Generally, the devices are made by wrapping a bifilar winding around a bobbin having a wick saturated with lithium chloride. When the winding is connected to a source of power, the electrical energy passing through the winding depends upon the resistance between the bifilar windings or across the wick. When the resistance is low, the current is such that the whole assembly is heated to increase the temperature of the wick to dry the wick. Upon an increased temperature, the resistance of the wick increases to cut down the current. The temperature of the assembly will reach an equilibrium temperature depending upon the moisture level of the surrounding air; therefore, the temperature is indicative of the air humidity level.

In such apparatuses, numerous ways have been devised to prevent the unit from reaching too high a temperature upon an initial operation. For example, resistances have been placed in series with the unit to limit the current, but in general the means heretofore used have had some disadvantages.

The present invention makes use of a transformer for the source of electrical energy or power. The transformer is designed to have a poor regulation such that the power output or voltage of the transformer will drop as the load increases on the transformer. When the humidity responsive device using the bifilar winding is connected to the secondary of the transformer and the wick is saturated with moisture, a large load is imposed on the transformer; however, the power delivered to the unit is maintained at a low level until the current requirement of the winding decreases to a level which would not cause harmful results to the unit.

An object of the present invention is to provide an improved apparatus for responding to the moisture level of a surrounding space wherein a poor regulation transformer is used as the source of electrical energy to prevent a large current flow when the resistance of the device is low.

The object will become apparent upon a study of the following specification and drawings, of which FIGURE 1 is a side sectional view of the present invention showing the moisture responsive element and the power source.

FIGURE 2 is a front cutaway view of the present invention.

FIGURE 3 is a graphical representation of the power characteristics of the transformer as shown in FIGURES l and 2.

FIGURE 4 is a schematic circuit of the present invention showing the moisture responsive element and the power source.

Referring to FIGURE 1, a case It has a main por- "ice tion covered by a cover 11. A tubular portion 12 attached to main portion 10. The tubular portion has a closed tube 13 attached with its open end to a hole in the main portion of case 10. Tubular portion 13 has a number of holes 14 for allowing moisture to enter from the space surrounding tube 13.

Case has a pair of terminals 15 and mounted in a manner to project outward to the left toward the front portion of cover 11. Terminals 15 and 20 are connected to a source of power by conventional conductors (not shown).

An assembly comprising a panel 21 has a pair of plugin type terminals 22 and 23 which are received by terminals 15 and 26, respectively. Mounted on panel 21 is a source of power or transformer 24 which has a primary winding 25 connected to a normal source of power by conductors and 31 which are connected to terminals 22 and 23, respectively. A secondary winding 32 is connected to another pair of terminals 33 and 34 mounted on panel 21 by conductors 35 and 40, respectively. A bobbin made of a steel tube 41 is connected at each end to a nylon circular plug member 42. The nylon member at the other end is not shown. Passing through the plug member 42 is a pair of connecting members 43 and 44 which are adapted to be received in terminals 33 and 34, respectively. An O-ring' 45 is mounted in the tubular portion 12 so that when the bobbin is inserted into the tube 13, a seal is provided between member 42 and the case.

Tube 41 is covered with an insulating lacquer or paint and then covered with a cloth 5% which is saturated with a solution of lithium chloride. Wound about the bobbin on top of the cloth layer is a bifilar winding 51-52 comprising a wire 51 and a wire 52 which are wound so that the adjacent portions of the wire are not touching and the electrical circuit between the two wires is completed by the resistance of the saline wick. When the panel 21 is inserted into the case 1% and bobbin 41 is placed into the tube 13, after being attached to panel 21, a pair of mounting screws 53 and 54 as shown in FIG- URE 2 hold the panel 21 forward into the case so that member 42 is in the opening of the tubular portion 12 of the case.

A temperature responsive element 55 which is shown as a bulb connected to some sort of liquid filled system by a capillary tube 69 is placed inside the tube 41 to respond to the temperature of the unit.

The output characteristic of the transformer 24 is shown in FIGURE 3. The characteristic is such. that as the load on the transformer increases, the voltage of the secondary decreases or droops. This type of transformer is old in the control field and is generally used with devices such as valves and thermostats to limit the current of the equipment when a short circuit exists. Upon a short circuit existing in a valve, the voltage to the valve would be de creased so that the current flowing to the valve would be maintained below some limit which would heat up the unit beyond a safe temperature. Such transformers have been required as a means of preventing equipment from burning up upon a short existing in the winding of valve actuator or relay. Such a current transformer is described on page 5-56 of Electrical Engineers Handbook, Third Edition 1947, Wiley Handbook Serieslohn Wiley and Sons Inc.

When the transformer is connected to the unit as shown schematically in FIGURE 4, the current flowing between wires 51 and 52 of the winding depends upon the resistance of the wick or cloth 5%. When the resistance is low, the current flowing will heat up the unit and the heat will dry the wick. As the wick dries, the resistance between wires 51 and 52 will decrease to cut down the amount of heat delivered to the unit. The operation of the unit results in an equilibrium temperature being estabo lished by the unit depending upon the moisture level of the air surrounding the unit.

When such a unit is used for the first time after an extended period of no use, element 50 may be quite moist and the resistance between Wires 51 and 52 very low. If the primary winding 25 is connected to a source of power, the power delivered to the wires 51-52 by the secondary 32, will be quite large and the current could be high enough to cause an excessive amount of heat in the unit resulting in some damage. By means of a transformer which has a regulation or characteristic as shown in FIG- URE 3, the operation is such that the amount of current which can be drawn by the Wires 51-52 is limited. As the unit heats up and the moisture level of element or wick 53 decreases to increase the resistance between wires 51 and 52, the output of the transformer will increase and a normal operation will be established. By means of the transformer 24, a very compact moisture responsive unit can be made up and a means for protecting the unit upon an initial warm-up period is provided without increasing the cost of the device by adding limiting resistors or other features to prevent the excessive current flowing when element 50 has a low resistance.

While the invention has been described in one specific manner, the intention is to limit the invention only by the scope of the claims, in which I claim:

1. In a moisture responsive device providing an output indicative of the moisture level in the surrounding air, a case having a main body and a ventilated tubular portion for insertion into a chamber, said case having terminals mounted thereon which are connected to a source of power, a bobbin covered by a layer of cloth saturated with lithium chloride, said layer having a resistance which varies with the moisture from the surrounding air absorbed by said lithium chloride, at least two wire windings wound on said bobbin in a bifilar manner, a plate, means for mounting said bobbin on said plate, a transformer having a primary and a secondary and being mounted on said plate, said transformer having a poor regulation characteristic in that an output of said secondary drops as the road increases to a predetermined vaiue, said plate being adapted to be received in said case so said bobbin is contained in said tubular portion, means including said terminals for connecting said primary to said source when said plate is placed in said case, temperature responsive means mounted inside said bobbin to respond to the temperature maintained by said windings, said responsive means having an output and circuit means connecting said windings to said secondary so that upon the initial energization of said windings when the resistance between said windings is low when said cloth contains a high amount of moisture the output of said transformer is maintained low to not burn out said windings by limiting the initial heating current, said bobbin increasing to a predetermined temperature depending upon the moisture level in said tubular portion so that the temperature and thus said output is an indication of the moisture content of said air.

2. In a device which provides a temperature characteristic depending upon the moisture content of the surrounding air, a bobbin covered with a layer of cloth saturated with lithium chloride, a pair of electrodes mounted on said bobbin so the resistance between said electrodes depends on the resistance of said saturated cloth, a transformer having a secondary winding with a drooping output characteristic as a load on said secondary winding increases, and electrical means connecting said pair of electrodes to said secondary whereby said bobbin is heated to increase said resistance to maintain an equilibrium temperature corresponding with the humidity of the surrounding air, said output being very small when said cloth is Wet and the resistance between said electrodes is low to limit the current flowing between said electrodes to prevent damage to the device.

References Cited in the file of this patent UNITED STATES PATENTS 2,359,278 Allen et al. Oct. 3, 1944- 2,754,378 Ohlheiser July 10, 1956 2,756,295 Schluchter July 24, 1956 

1. IN A MOISTURE RESPONSIVE DEVICE PROVIDING AN OUTPUT INDICATIVE OF THE MOISTURE LEVEL IN THE SURROUNDING AIR, A CASE HAVING A MAIN BODY AND VENTILATED TUBULAR PORTION FOR INSERTION INTO A CHAMBER, SAID CASE HAVING TERMINALS MOUNTED THEREON WHICH ARE CONNECTED TO A SOURCE OF POWER, A BOBBIN COVERED BY A LAYER OF CLOTH SATURATED WITH LITHIUM CHLORIDE, SAID LAYER HAVING A RESISTANCE WHICH VARIES WITH THE MOISTURE FROM THE SURROUNDING AIR ABSORBED BY SAID LITHIUM CHLORIDE, AT LEAST TWO WIRE WINDINGS WOUND ON SAID BOBBIN IN A BIFILAR MANNER, A PLATE, MEANS FOR MOUNTING SAID BOBBIN ON SMALL PLATE, A TRANSFORMER HAVING A PRIMARY AND A SECONDARY AND BEING MOUNTED ON SAID PLATE, SAID TRANSFORMER HAVING A POOR REGULATION CHARACTERISTIC IN THAT AN OUTPUT OF SAID SECONDARY DROPS AS THE LOAD INCREASES TO A PREDETERMINED VALUE, SAID PLATE BEING ADAPTED TO BE RECEIVED IN SAID CASE SO SAID BOBBIN IS CONTAINED IN SAID TUBULAR PORTION, MEANS INCLUDING SAID TERMINALS FOR CONNECTING SAID PRIMARY TO SAID SOURCE WHEN SAID PLATE IS PLACED IN SAID CASE, TEMPERATURE RESPONSIVE MEANS MOUNTED INSIDE SAID BOBBIN TO RESPOND TO THE TEMPERATURE MAINTAINED BY SAID WINDINGS, SAID RESPONSIVE MEANS HAVING AN OUTPUT AND CIRCUIT MEANS CONNECTING SAID WINDINGS TO SAID SECONDARY SO THAT UPON THE INITIAL ENERGIZATION OF SAID WINDINGS WHEN THE RESISTANCE BETWEEN SAID WINDINGS IS LOW WHEN SAID CLOTH CONTAINS A HIGH AMOUNT OF MOISTURE THE OUTPUT OF SAID TRANSFORMER IS MAINTAINED LOW TO NOT BURN OUT SAID WINDINGS BY LIMITING THE INITIAL HEATING CURRENT, SAID BOBBIN INCREASING TO A PREDETERMINED TEMPERATURE DEPENDING UPON THE MOISTURE LEVEL IN SAID TUBULAR PORTION SO THAT THE TEMPERATURE AND THUS SAID OUTPUT IS AN INDICATION OF THE MOISTURE CONTENT OF SAID AIR. 